General information

    Genetics as a science emerged as a result of practical needs.  In breeding domestic animals and cultivated plants, crossbreeding of organisms belonging to different species, breeds, varieties and differing from each other in some way has long been used. By comparing hybrids with the original forms, practitioners have long noticed some peculiarities of trait inheritance.Genetic patterns are the basis for breeding, i.e., the creation of new and improvement of existing breeds of domestic animals, varieties of cultivated plants, and microorganisms used in the pharmaceutical industry, medicine, and agriculture. Genetics is of great importance for medicine and veterinary medicine, as many human and animal diseases are hereditary and require genetic research to treat or prevent them.

    The basic laws of inheritance of properties and traits were discovered by G. Mendel (1822-1884). However, these studies were not immediately properly appreciated and remained little known until 1900, when three researchers (G. de Vries in Holland, T. Correns in Germany, and E. Cher-mack in Austria) independently rediscovered the laws of heredity formulated by Mendel.

    Each trait of an organism is determined by one or more genes. Each gene can exist in several forms (states) called alleles. The alleles of a gene are located in homologous (similar, identical) chromosomes in the same places (loci). Genes can be in dominant (dominant influence on a trait) or recessive (manifested on a trait in the absence of dominant) states (forms). If an organism has identical genes in dominant or recessive states, then such an organism is called a homozygote. Depending on the state of the gene in a homozygous organism (dominant or recessive), homozygotes are divided into dominant homozygotes and recessive homozygotes. If an organism has both a dominant gene for a given trait and a recessive gene, such an organism is called a heterozygote.

    A set of hereditary factors of an organism (genes) is called a genotype. The set of all signs and properties of an organism that are the result of the interaction of the genotype and the environment is called the phenotype. That is, the phenotype is a reflection of the genotype in combination with the environment. The limits within which the environment affects the manifestation of the genotype are called the norm of reaction.